Selecting a network slice identifier

ABSTRACT

During PDN connection establishment in the EPC, a UE and a session managment entity (SME) (e.g., PGW-C+SMF) exchange information. In case the SME supports more than one S-NSSAI, before the SME provides an S-NSSAI to the UE, the SME should check such that the selected S-NSSAI is among the UE&#39;s subscribed S-NSSAIs by retrieving the Subscribed S-NSSAI from a UDM using, for example, the Nudm_SDM_Get service operation.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of International patent applicationno. PCT/IB2019/055851, filed on Jul. 9, 2019, which claims priority toU.S. provisional patent application No. 62/769,453, filed on Nov. 19,2018; this application also claims the benefit of U.S. provisionalpatent application No. 62/769,453, filed on Nov. 19, 2018. The aboveidentified applications are incorporated by this reference.

TECHNICAL FIELD

Disclosed are embodiments related to connecting selecting a networkslice identifier.

BACKGROUND

The Third Generation Partnership Project (3GPP) is working on thedevelopment and design of the next generation mobile communicationssystem (a.k.a., the 5G mobile communication system or the NextGeneration (NG) system or simply “5GS” or “NG” for short). 3GPP iscurrently in the process of specifying the 5G radio interface called NewRadio (NR) or “5G-RAN” as well as a Next Generation Packet Core Network(NG-CN or 5GC). 5GS is a new system that is different from the legacyEvolved Packet System (EPS) also when EPS is extended to support the new5G radio access named New Radio (NR).

A user equipment (UE) (i.e., a device capable of wireless communicationwith a radio access network node, such as, for example, a smartphone, alaptop, a tablet, a smart sensor, an appliance, etc.) needs to registerwith a network in order to receive services which require registration.A registration procedure is utilized in the following situations: (1)when the UE initially registers to a 5G system; (2) when the UEinitiates a registration procedure due to mobility, e.g. when the UEchanges to a new Tracking Area (TA) in idle mode; (3) when the UEperforms a periodic update due to expiration of a predefined time periodof inactivity, etc.

As part of the 5G work in 3GPP, a network slice has been described as alogical network that provides specific network capabilities and networkcharacteristics, and a network slice instance as a set of networkfunction instances and the required resources (e.g. compute, storage andnetworking resources) which form a deployed network slice. Furtherdetails on network slicing are described in 3GPP TS 23.501, v1.0.0(2017-06) “3rd Generation Partnership Project; Technical SpecificationGroup Services and System Aspects; System Architecture for the 5GSystem; Stage 2” (Release 15) (“3GPP TS 23.501”), and specificallyclause 5.15 Network Slicing.

By way of background, according to 3GPP TS 23.501, clause 5.15.1,“Network slices may differ for supported features and network functionsoptimisations. The operator may deploy multiple Network Slice instancesdelivering exactly the same features but for different groups of UEs,e.g. as they deliver a different committed service and/or because theymay be dedicated to a customer. A single UE can simultaneously be servedby one or more Network Slice instances via a 5G-AN. A single UE may beserved by at most 8 Network Slices at a time. The AMF instance servingthe UE logically belongs to each of the Network Slice instances servingthe UE, i.e. this AMF instance is common to the Network Slice instancesserving a UE.”

An S-NSSAI (Single Network Slice Selection Assistance Information)identifies a Network Slice, and an NSSAI is a list of S-NSSAIs. Morespecifically, an S-NSSAI contains a slice / service type (SST) and mayalso contain a slice differentiator (SD). Further, as provided in 3GPPTS 23.501, clause 5.15.2.1: “The (R)AN may use Requested NSSAI in accessstratum signalling to handle the UE Control Plane connection before the5GC informs the (R)AN of the Allowed NSSAI. The Requested NSSAI is notused by the RAN for routing when the UE provides also a Temporary UserID. . . . When a UE is successfully registered, the CN informs the (R)ANby providing the whole Allowed NSSAI for the Control Plane aspects.”

Each S-NSSAI may have a standardized value or a public land mobilenetwork (PLMN) specific value. Where the S-NSSAI has a PLMN-specificvalue, the PLMN-specific value is associated to a PLMN ID of the PLMNthat assigns it.

Regarding the storage of NSSAI (collection of S-NSSAIs) in the UE,clause 5.15.4 of TS 23.501 states the following: “A UE can be configuredby the HPLMN [home PLMN] with a Configured NSSAI per PLMN. A ConfiguredNSSAI can be PLMN-specific and the HPLMN indicates to what PLMN(s) eachConfigured NSSAI applies, including whether the Configured NSSAI appliesto all PLMNs, i. e. the Configured NSSAI conveys the same informationregardless of the PLMN the UE is accessing (e.g. this could be possiblefor NSSAIs containing only standardized S-NSSAIs). When providing aRequested NSSAI to the network upon registration, the UE in a given PLMNshall only use S-NSSAIs belonging to the Configured NSSAI, if any, ofthat PLMN. Upon successful completion of a UE's Registration procedure,the UE may obtain from the AMF an Allowed NSSAI for this PLMN, which mayinclude one or more S-NSSAIs. . . . For each PLMN, the UE shall storethe Configured NSSAI and, if any, the Allowed NSSAI. When the UEreceives an Allowed NSSAI for a PLMN, it shall store it and override anypreviously stored Allowed NSSAI for this PLMN.”

Particularly for roaming the TS 23.501 clause 5.15.6 stipulates that:“For roaming scenarios, the Network Slice specific network functions inVPLMN and HPLMN are selected based on the S-NSSAI provided by the UEduring PDU connection establishment as following. If a standardizedS-NSSAI is used, then selections of slice specific NF instances are doneby each PLMN based on the provided S-NSSAI; Otherwise, the VPLMN mapsthe S-NSSAI of HPLMN to a S-NSSAI of VPLMN based on roaming agreement(including mapping to a default S-NSSAI of VPLMN). The selection ofslice specific NF instance in VPLMN are done based on the S-NSSAI ofVPLMN, and the selection of any slice specific NF instance in HPLMN arebased on the S-NSSAI of HPLMN.”

SUMMARY

There is a need to provide for interworking between 5GS and legacysystems. For example, an issue is that a PGW-C+ SMF (which may supportmore than one S-NSSAI) does not know which are the Subscribed S-NSSAIsfor a UE (in case a non-subscribed S-NSSAI is returned the PDNConnection will be released when moving to 5GS). Therefore, thePGW-C+SMF would need to ensure that the S-NSSAI provided to the UE is aSubscribed S-NSSAI (and also do a mapping to VPLMN value in case PGW-C +SMF is located in a VPLMN).

Accordingly, in one aspect there is provided a method that includes asession management entity transmitting to a data management function arequest for a set of subscribed network slice identifiers identifyingone or more network slices to which a UE is subscribed. The methodfurther includes the session management entity receiving, from the datamanagement function, a first set of network slice identifiers to whichthe UE is subscribed. The method also includes the session managemententity selecting a network slice identifier and transmitting, to the UE,a message indicating the selected network slice identifier. The step ofselecting the network slice identifier comprises either: i) selecting,from the received first set of network slice identifiers to which the UEis subscribed, a network slice identifier that is supported by thesession management entity or ii) selecting a network slice identifierthat is supported by the session management entity, the selected networkslice identifier being selected from a second set of network sliceidentifiers to which the first set of network slice identifiers aremapped.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments.

FIG. 1 diagrams an exemplary message flow for allocating a network sliceaccording to some embodiments.

FIG. 2 shows an exemplary method for allocating a network sliceaccording to some embodiments.

FIG. 3 is a block diagram of an apparatus 300, according to someembodiments, for implementing a session management node.

DETAILED DESCRIPTION

For a UE being served by Evolved Packet System (EPS) and withestablished protocol data network (PDN) connections, there are threedifferent scenarios for a data connection (e.g., a PDN connection): 1)the UE may be served in its home network; 2) the UE may be served in avisited network with home routed traffic; or 3) the UE may be served ina visited network with local breakout (LBO).

A UE may be transferred from EPS to 5GS from any of these cases. Intransferring the UE to 5GS, it is desirable to avoid releasing the UE'scurrent PDN connections. In each of the three cases noted above where aUE has surviving PDN connections when moving to 5GS, a sessionmanagement node (e.g., a combined Packet Data Network Gateway Control(PGW-C)+Session Management Function (SMF)) may be used. During PDNConnection establishment, the UE may allocate a respective PDU SessionID and send it to the session management node (for example, via aprotocol configuration options (PCO) information element). A networkslice identifier (e.g., a S-NSSAI) associated with each PDN connectionmay be determined based on the operator policy by the session managementnode. For example, the session management node may determine the networkslice identifier based on a combination of a session management nodeaddress and an access point name (APN). The determined network sliceidentifier may be sent to the UE in a message (e.g., a PCO) togetherwith a PLMN ID to which the network slice identifier relates. Thisprocess is generally described in clause 5.15.7.1 of 3GPP TS 23.501v15.3.0, which is incorporated by reference herein.

When UE moves from EPS to 5GS, the UE may include the network sliceidentifiers (with values for the Serving PLMN of the target 5GS, ifavailable) associated with the established PDN connections in theRequested NSSAI in RRC Connection Establishment and NAS. The UE may alsoprovide to the AMF in the Registration Request message the mappinginformation as described in clause 5.15.6. This process is generallydescribed in clause 5.15.7.2 of 3GPP TS 23.501 v15.3.0.

In cases 1 and 2, the session management node may transmit to the UEnetwork slice identifiers that are valid in the UE's home network (e.g.,home network S-NSSAI(s)/hS-NSSAI(s)).

In case 3, the session management node may transmit to the UE networkslice identifiers that are valid in the visited network (e.g., visitednetwork S-NSSAI(s)/vS-NSSAI(s)).

Without checking the UE's subscription information to confirm that anallocated network slice is allowed, there is a risk at mobility from EPSto 5GS that one or more of the UE's PDU sessions may be released. Thenetwork slice identifier received by the UE from the session managementnode may be transmitted by the UE to an AMF. The AMF may then attempt toverify that the UE is allowed to use the identified network slice(s). Ifthe identified network slice(s) are not allowed, the AMF may release therespective PDU sessions. It is possible to avoid this negative outcomein a case where the session management node supports at least onenetwork slice that is also allowed according to the UE's subscriptioninformation. Accordingly, there is a need for a session management nodethat can ensure that an allocated network slice identifier is allowedaccording to the UEs subscription information.

FIG. 1 diagrams an exemplary message flow for allocating a network slicewhen moving a UE from a legacy network to 5GS. At step 112, a sessionmanagement node 102 (also referred to as a session management entity(SME) 102) receives a request to allocate one or more network sliceidentifiers. In some embodiments, the request 112 may be received,directly or indirectly, from a UE. In some embodiments, the request 112may be a Create Session Request. In some embodiments, the sessionmanagement node may be a Session Management Function in 5GS, a PGW inEPS, or a combination thereof (e.g., a PGW-C+SMF). At step 114, thesession management node 102 may transmit to a data management function104 a request for network slice identifiers to which the UE issubscribed. In some embodiments, this step is only performed if node 102supports more than one network slice identifier. The data managementfunction 104 may store or have access to subscription information forthe UE. In some embodiments, the data management function 104 may be aUnified Data Management Function. At step 116, the session managementnode 102 may receive from the data management function 104 a response tothe request 114 for subscribed network slice identifiers. The response116 may include a set of one or more identifiers which may, for example,identify one or more network slices that the UE is allowed to use. Forexample, the response may include a set of hS-NSSAIs for the UE (anhS-NSSAI is an S-NSSAI that is valid in the UE's home network). In someembodiments, steps 114 and 116 may be achieved by letting the sessionmanagement node 102 use the Nudm_SDM_Get (SUPI, Slice SelectionSubscription data) service, which is available to the AMF in currentversions of 5GS standards.

If the UE is served in its home network or in a visited network withhome routed traffic (i.e., in cases 1 or 2), the session management node102 may select a network slice identifier from among the network sliceidentifiers received in response 116. The session management node 102preferably selects a network slice identifier that is both (i) among thereceived set of network slice identifiers, and (ii) supported by thesession management node 102. If no network slice identifier satisfyingboth conditions exists, the session management node 102 may insteadselect from among the network slice identifiers that are supported bythe session management node 102. In this case, the session managementnode 102 may notify the operator(s) of the UE's home network and/or thevisiting network that a node meeting both selection criteria (authorizedfor use by the UE and supported by the node 102) could not bedetermined.

If the UE is served in a visited network with local breakout (LBO)(i.e., in case 3), however, the session management node 102 may performoptional step 118 to determine a network slice identifier for thevisiting network (e.g., a vS-NSSAI) that is mapped to the network sliceidentifier (e.g., a hS-NSSAI) received from the data managementfunction. In step 118, the session management node 102 may transmit to aslice selection function 106 (e.g., a Network Slice Selection Function(NSSF)) a request for visiting network slice identifiers that correspondto one or more of the home network slice identifiers received from thedata management function 104. In some embodiments, the request 118 mayinclude one, some, or all of the network slice identifiers received inresponse 116 from the data management function. In step 120, the sessionmanagement node 102 may receive from the slice selection function 106 aresponse indicating a set of one or more visiting network sliceidentifiers that correspond to the home network slice identifierstransmitted in request 118. In some embodiments, the slice selectionfunction 106 may determine visiting slice identifiers by referencing anindexing table in which slice identifiers for one network operator aremapped to slice identifiers for another network operator. The result ofthat mapping operation may be transmitted to the session management node102 in response 120. In some embodiments, to get the mapping betweensubscribed S-NSSAIs and corresponding vS-NSSAIs (i.e., S-NSSAIs valid inthe visited network corresponding to the subscribed S-NSSAIs), anadjusted version of the Nnssf_NSSelection_Get service from the NSSF maybe used. The service may be available from the PGW-C+SMF and asinput/output it should be possible to provide a subscribed S-NSSAI(e.g., a network slice identifier received in step 114).

In case 3, the session management node 102 may then select a networkslice identifier that is both (i) supported by the session managementnode 102, and (ii) among the set of visiting network slice identifiersreceived from the slice selection function 106. In this sense, theselected identifier may be from among a second set of network sliceidentifiers that corresponds to the first set of network sliceidentifiers received from the data management function. As discussedabove, if no such node exists, the session management node 102 mayinstead select from among the network slice identifiers that aresupported by the session management node 102. In this case, the sessionmanagement node 102 may notify the operator(s) of the UE's home networkand/or the visiting network that a node meeting both selection criteria(mapped to a subscribed slice identifier and supported by the node 102)could not be determined.

In any of cases 1, 2, and 3, the session management node 102 may thentransmit the selected network slice identifier(s), directly orindirectly, to the UE per step 122. In some embodiments, thisinformation may be included in a PCO. In some embodiments, theinformation may be transmitted in a Create Session Response. In someembodiments, the UE may be served by the session management node 102 ina second network (e.g., a 3G or 4G network) at the time that the request112 is received. In some embodiments, the UE has existing data networkconnections (e.g., PDN connections), and the request 112 is transmitted,directly or indirectly, from the UE and includes a session identifieridentifying one or more of the UE's PDN connections. In someembodiments, the message 122 transmitted to the UE may indicate that theselected network slice identifier(s) are associated with respecting PDNconnection(s) of the UE. In some embodiments, one respective selectednetwork slice identifier may be transmitted to the UE for each of theUE's PDN connection(s).

In sum, for case 1 and 2, the procedure in a combined PGW-C+SMF may looklike: 1. Fetch subscribed S-NSSAIs (hS-NSSAIs) from UDM; 2. Select ah-NSSAI from the hS-NSSAIs acquired in step 1 and include it in the PCOto the UE at PDN connection establishment.

For case 3, the procedure in a combined PGW-C+SMF may look like: 1.Fetch subscribed S-NSSAIs (hS-NSSAIs) from UDM; 2. Get correspondingvS-NSSAI for each subscribed S-NSSAI by querying the NSSF; 3. Select avS-NSSAI from the vS-NSSAIs acquired in step 2 and include it in the PCOto the UE at PDN connection establishment.

In summary, the PGW-C+SMF may retrieve a Subscribed S-NSSAI to comparewith the S-NSSAIs the PGW-C+SMF supports/serves and then decides whichof these to use and send towards the UE in PCO.

FIG. 2 shows a flowchart for a method 200, which generally reflects tothe steps performed by the session management node 102 in the diagramshown in FIG. 1. In step 202, the session management node may transmit,to a data management function, a request for a set of network sliceidentifiers to which the UE is subscribed. In step 204, the sessionmanagement node may receive, from a data management function, a set ofnetwork slice identifiers. The set of network slice identifiers mayindicate one or more network slices to which the UE is subscribed.Blocks 206 and 208 show optional steps which may be performed in a casewhere a data connection is routed through a visiting network using LBO.In optional step 206, the session management node may transmit, to aslice selection function, at least one of the network slice identifiers(e.g., hS-NSSAIs) received from the data management function. In someembodiments, more than one or all of the received identifiers (e.g.,hS-NSSAIs) may be transmitted to the slice selection function. Inoptional step 208, the session management node may receive, from theslice selection function, a second network slice identifier. In someembodiments, the second network slice identifier may identify a slice inthe visiting network (for example, the second network slice identifiermay be a vS-NSSAI). In some embodiments, the session management node mayreceive a respective visiting network slice identifier for each of thehome network slice identifiers transmitted in step 206. In someembodiments, each received visiting slice identifier may correspond to arespective home network slice identifier in indexing table in whichslice identifiers for one network operator are mapped to sliceidentifiers for another network operator.

In step 210, the session management node may select a network sliceidentifier. In cases 1 and 2, the session management node may select anidentifier that is both (i) supported by the session management node,and (ii) among the set of identifiers received from the data managementfunction. For example, the session management node may determine thatthe first network slice identifier matches one of a plurality of networkslice identifiers identifying a network slice supported by the sessionmanagement node, and select a first network slice identifier from amongthe set of identifiers received from the data management function.

In case 3, the session management node may select an identifier that isboth (i) supported by the session management node, and (ii) among theset of identifiers received from the slice selection function. Forexample, the session management node may determine that the secondnetwork slice identifier received from the slice selection functionmatches one of a plurality of network slice identifiers identifying anetwork slice supported by the session management node, and the selectthe second slice identifier.

FIG. 3 is a block diagram of an apparatus 300, according to someembodiments, for implementing the session management node 102. As shownin FIG. 3, apparatus 300 may comprise: processing circuitry (PC) 302,which may include one or more processors (P) 355 (e.g., a generalpurpose microprocessor and/or one or more other processors, such as anapplication specific integrated circuit (ASIC), field-programmable gatearrays (FPGAs), and the like), which processors may be co-located in asingle housing or in a single data center or may be geographicallydistributed; a network interface 348 comprising a transmitter (Tx) 345and a receiver (Rx) 347 for enabling apparatus 300 to transmit data toand receive data from other nodes connected to a network 110 (e.g., anInternet Protocol (IP) network) to which network interface 348 isconnected; and a local storage unit (a.k.a., “data storage system”) 308,which may include one or more non-volatile storage devices and/or one ormore volatile storage devices. In embodiments where PC 302 includes aprogrammable processor, a computer program product (CPP) 341 may beprovided. CPP 341 includes a computer readable medium (CRM) 342 storinga computer program (CP) 343 comprising computer readable instructions(CRI) 344. CRM 342 may be a non-transitory computer readable medium,such as, magnetic media (e.g., a hard disk), optical media, memorydevices (e.g., random access memory, flash memory), and the like. Insome embodiments, the CRI 344 of computer program 343 is configured suchthat when executed by PC 302, the CRI causes apparatus 300 to performsteps described herein (e.g., steps described herein with reference tothe flow charts). In other embodiments, apparatus 300 may be configuredto perform steps described herein without the need for code. That is,for example, PC 302 may consist merely of one or more ASICs. Hence, thefeatures of the embodiments described herein may be implemented inhardware and/or software.

Appendix A from the Provisional Patent Application

The provisional patent application to which this application claimspriority included an Appendix A, which is reproduced in relevant partbelow:

Change Request

Reason for change: at PDN Connection establishment in a combinedPGW-C+SMF an S-NSSAI shall be allocated in preparation for a move to 5GS(refer to 23.501 clause 5.15.7.1). The combined PGW-C+SMF should ensurethat the allocated S-NSSAI is allowed according to the UEs subscribedS-NSSAIs.

Summary of change: 1) Make the Nudm_SDM_Get (SUPI, Slice SelectionSubscription data) service available also by SMF; and 2) Make theNnssf_NSSelection_Get service available also by PGW-C+SMF. Make itpossible to use subscribed S-NSSAIs as input/output instead of “S-NSSAIsfor the HPLMN associated with established PDN connection.”

Consequences if not approved: There is a risk at mobility from EPS to5GS that AMF needs to release PDU Session(s) associated to S-NSSAI(s)not allowed according to the UEs subscribed S-NSSAIs.

4.11.0a Impacts to EPS Procedues

4.11.0a.1 General

This clause captures changes to procedures in TS 23.401 [13] that arecommon to interworking based on N26 and interworking without N26.

4.11.0a.2 Interaction with PCC

When interworking with 5GS is supported and a “PGW-C+SMF” is selectedfor a UE, policy interactions between PDN GW and PCRF specified in TS23.401 [13] are replaced by equivalent interactions between PGW-C+SMFand PCRF+PCF as follows:

-   -   (PCEF initiated) IP-CAN Session Establishment procedure is        replaced by SM Policy Association Establishment Procedure as        described in clause 4.16.4.    -   IP-CAN Session Modification procedure is replaced by SM Policy        Association Modification procedure as described in clause        4.16.5.    -   IP-CAN Session Termination procedure is replaced by SM Policy        Association Termination procedure as described in clause 4.16.6.

4.11.0a.3 Mobility Restrictions

The UE's subscription may include access restriction for NR in 5GS andrestriction for Core Network Type (5GC). If so, the HSS provides theserestrictions to the MME. The MME includes these restrictions in theHandover Restriction List to the E-UTRAN. The MME and E-UTRAN use theserestrictions to determine if mobility of the UE to 5GS or NR connectedto 5GS should be permitted.

4.11.0a.4 PGW Selection

When the UE requests to establish a PDN connection to an APN, the MMEmay use the UE's support for 5GC NAS indication included in the UENetwork Capability and/or UE's subscription from HSS that includes UE'smobility restriction paramters related to 5GS and/or indication ofsupport for interworking with 5GS for this APN to determine if PGW-C+SMFor a standalone PGW-C should be selected.

If restriction for Core Network Type indicates that the UE can access to5GC, it implies that the UE has 5G subscription data.

4.11.0a.5 PDN Connection Establishment

During PDN connection establishment in the EPC, the UE and the PGW-C+SMFexchange information via PCO as described in 23.501 [2] clause 5.15.7.In case the PGW-C+SMF supports more than one S-NSSAI, before thePGW-C+SMF provides an S-NSSAI to the UE, the PGW-C+SMF should check suchthat the selected S-NSSAI is among the UEs subscribed S-NSSAIs byretrieving the Subscribed S-NSSAI from UDM using the Nudm_SDM_Getservice operation. If the PGW-C+SMF is in a VPLMN, the PGW-C+SMF usesthe Nnssf_NSSelection_Get service operation to retrieve a mapping of theSubscribed S-NSSAIs to Serving PLMN S-NSSAI values.

5.2.3.3.1 General

Subscription data types used in the Nudm_SubscriberDataManagementService are defined in Table 5.2.3.3.1-1 below.

TABLE 5.2.3.3.1-1 UE Subscription data types Subscription data typeField Description Access and Mobility GPSI List List of the GPSI(Generic Public Subscription Subscription data Identifier) used bothinside and outside of the (data needed for UE 3GPP system to address a3GPP subscription. Registration and Internal Group ID-list List of thesubscribed internal group(s) that the Mobility UE belongs to.Management) Subscribed-UE-AMBR The Maximum Aggregated uplink anddownlink MBRs to be shared across all Non-GBR QoS Flows according to thesubscription of the user. Subscribed S-NSSAIs The Network Slices thatthe UE subscribes to. In the roaming case, it indicates the subscribedNetwork Slices applicable to the Serving PLMN. Default S-NSSAIs TheSubscribed S-NSSAIs marked as default S- NSSAI. In the roaming case,only those applicable to the Serving PLMN. UE Usage Type As defined inTS 23.501 [2], clause 5.15.7.2. RAT restriction 3GPP Radio AccessTechnology(ies) not allowed the UE to access. Forbidden area Definesareas in which the UE is not permitted to initiate any communicationwith the network. Service Area Restriction Indicates Allowed areas inwhich the UE is permitted to initiate communication with the network,and Non-allowed areas in which the UE and the network are not allowed toinitiate Service Request or SM signalling to obtain user services. CoreNetwork type restriction Defines whether UE is allowed to connect to SGCand/or EPC for this PLMN. RFSP Index An index to specific RRMconfiguration in the NG- RAN. Subscribed Periodic Indicates a subscribedPeriodic Registration Registration Timer Timer value. Priority ServicesIndicates the user is subscribed to priority service (MPS) as indicatedin TS 23.501 [2], clause 5.16.5. UE behavioural information/ Informationon expected UE movement and Communication patterns communicationcharacteristics. See clause 4.15.6.2 Steering of Roaming List ofpreferred PLMN/access technology combinations or HPLMN indication thatno change of the “Operator Controlled PLMN Selector with AccessTechnology” list stored in the UE is needed (see NOTE 3). Optionallyincludes an indication that the UDM requests an acknowledgement of thereception of this information from the UE. Network Slicing SubcriptionWhen present, indicates to the serving AMF that Change Indicator thesubscription data for network slicing changed and the UE configurationmust be updated. Tracing Requirements Trace requirements about a UE(e.g. trace reference, address of the Trace Collection Entity, etc.) isdefined in TS 32.421 [39]. This information is only sent to AMF in theHPLMN or one of its equivalent PLMN(s). Slice Selection SubscribedS-NSSAIs The Network Slices that the UE subscribes to. In Subscriptiondata roaming case, it indicates the subscribed network (data needed forSlice slices applicable to the serving PLMN. Selection as described inclause 4.2.2.2.3 and in clause 4.11.0a.5) UE context in AMF AMFAllocated AMF for the registered UE. Include AMF data address and AMF NFId. Access Type 3GPP or non-3GPP access through this AMF HomogenousSupport of IMS Indicates per UE and AMF if “IMS Voice over PS Voice overPS Sessions for Sessions” is homogeneously supported in all TAs AMF inthe serving AMF or homogeneously not supported, or, support is non-homogeneous/unknown, see clause 5.16.3.3 of TS 23.501 [2]. SMF SelectionSUPI Key Subscription data SMF Selection Subscription data contains oneor more S-NSSAI level (data needed for SMF subscription data: Selectionas S-NSSAI Indicates the value of the S-NSSAI. described in clause 6.3.2of Subscribed DNN list List of the subscribed DNNs for the UE (NOTE 1).TS 23.501 [2]) Default DNN The default DNN if the UE does not provide aDNN (NOTE 2). LBO Roaming Information Indicates whether LBO roaming isallowed per DNN, or per (S-NSSAI, subscribed DNN) lnterworking with EPSindication Indicates for which DNN from the Subscribed list DNN listinterworking is supported. UE context in SMF SUPI Key data PDU SessionId(s) List of PDU Session Id(s) for the UE For each PDU Session Id: DNNDNN for the PDU Session. SMF Allocated SMF for the PDU Session. IncludesSMF IP Address and SMF NF Id. SMS Management SMS parameters IndicatesSMS parameters subscribed for SMS Subscription data service such as SMSteleservice, SMS barring list (data needed by SMSF for SMSF TraceRequirements Trace requirements about a UE (e.g. trace Registration)reference, address of the Trace Collection Entity, etc.) is defined inTS 32.421 [39]. This information is only sent to a SMSF in HPLMN. SMSSubscription SMS Subscription Indicates subscription to any SMS deliveryservice data (data needed over NAS irrespective of access type. in AMF)UE Context in SMSF SMSF Information Indicates SMSF allocated for the UE,including data SMSF address and SMSF NF ID. Access Type 3GPP or non-3GPPaccess through this SMSF Session Management GPSI List List of the GPSI(Generic Public Subscription Subscription data Identifier) used bothinside and outside of the (data needed for PDU 3GPP system to address a3GPP subscription. Session Internal Group ID-list List of the subscribedinternal group(s) that the Establishment) UE belongs to. TraceRequirements Trace requirements about a UE (e.g. trace reference,address of the Trace Collection Entity, etc...) is defined in TS 32.421[39]. This information is only sent to a SMF in the HPLMN or one of itsequivalent PLMN(s). Session Management Subscription data contains one ormore S-NSSAI level subscription data: S-NSSAI Indicates the value of theS-NSSAI. Subscribed DNN list List of the subscribed DNNs for the S-NSSAI(NOTE 1). For each DNN in S-NSSAI level subscription data: DNN DNN forthe PDU Session. UE Address Indicates the subscribed static IPaddress(es) for the IPv4 or IPv6 or IPv4v6 type PDU Sessions accessingthe DNN, S-NSSAI. Allowed PDU Session Types Indicates the allowed PDUSession Types (IPv4, IPv6, IPv4v6, Ethernet, and Unstructured) for theDNN, S-NSSAI. Default PDU Session Type Indicates the default PDU SessionType for the DNN, S-NSSAI. Allowed SSC modes Indicates the allowed SSCmodes for the DNN, S- NSSAI. Default SSC mode Indicate the default SSCmode for the DNN, S- NSSAI. Interworking with EPS indication Indicateswhether interworking with EPS is supported for this DNN and S-NSSAI. 5GS Subscribed QoS profile The QoS Flow level QoS parameter values (5QIand ARP) for the DNN, S-NSSAI (see clause 5.7.2.7 of TS 23.501 [2]).Charging Characteristics This information is defined in TS 32.240 [34];it may e.g. contain information on how to contact the Charging Function.This information, when provided shall override any correspondingpredefined information at the SMF Subscribed-Session-AMBR The maximumaggregated uplink and downlink MBRs to be shared across all Non-GBR QoSFlows in each PDU Session, which are established for the DNN, S-NSSAI.Static IP address/prefix Indicate the static IP address/prefix for theDNN, S-NSSAI. User Plane Security Policy Indicates the security policyfor integrity protection and encryption for the user plane. Identifiertranslation SUPI Corresponding SUPI for input GPSI (Optional) MSISDNCorresponding GPSI (MSISDN) for input GPSI (External Identifier). Thisis optionally provided for legacy SMS infrastructure not supportingMSISDN-less SMS. The presence of an MSISDN should be interpreted as anindication to the NEF that MSISDN shall be used to identify the UE whensending the SMS to the SMS-SC via T4. Intersystem continuity (DNN, PGWFQDN) list For each DNN, indicates the PGW-C + SMF which Context supportinterworking with EPC. NOTE 1: The Subscribed DNN list can include awildcard DNN. NOTE 2: The default DNN shall not be a wildcard DNN. NOTE3: The Steering of Roaming information is protected using the mechanismsdefined in TS 33.501 [15].

TABLE 5.2.3.3.1-2 Group Subscription data types Subscription data typeField Description Group ldentifer External Group Identifier Identifiesexternal group of UEs that the UE translation belongs to as defined inTS 23.682 [23] (Optional) Internal Group Identifies internal group ofUEs that the UE Identifier belongs to as defined in TS 23.501 [2] SUPIlist Corresponding SUPI list for input External Group Identifier

At least a mandatory key is required for each Subscription Data Type toidentify the corresponding data. Depending on the use case, for someSubscription Data Types it is possible to use one or multiple sub keysto further identify the corresponding data, as defined in Tables5.2.3.3.1-3 and 5.2.3.3.1-4 below:

TABLE 5.2.3.3.1-3 UE Subscription data types keys Subscription DataTypes Data Key Data Sub Key Access and Mobility Subscription data SUPI —SMF Selection Subscription data SUPI — UE context in SMF data SUPIS-NSSAI SMS Management Subscription data SUPI — SMS Subscription dataSUPI UE Context in SMSF data SUPI Session Management Subscription dataSUPI S-NSSAI DNN Identifier translation GPSI — Slice SelectionSubscription data SUPI — Intersystem continuity Context SUPI DNN

TABLE 5.2.3.3.1-4 Group Subscription data types keys Subscription DataTypes Data Key Data Sub Key Group Identifier translation External GroupIdentifier

5.2.3.3.2 Nudm_SDM_Get Service Operation

Service Operation name: Nudm_SDM_Get.

Description: Consumer NF gets the subscriber data indicated by thesubscription data type input from UDM. The UDM shall check the requestedconsumer is authorized to get the specific subscription data requested.In case of NF consumer is SMF, the subscriber data may contain e.g.Allowed PDU Session Type(s), Allowed SSC mode(s), default 5QI/ARP,Subscribed S-NSSAI(s).

Inputs, Required: NF ID, Subscription data type(s), Key for eachSubscription data type(s).

Inputs, Optional: Data Sub Key(s).

Outputs, Required: The consumer NF gets the requested subscription data.

Outputs, Optional: None.

5.2.16.2 Nnssf_NSSelection Service

5.2.16.2.1 Nnssf_NSSelection_Get Service Operation

Service Operation Name: Nnssf_NSSelection_Get

Description: This service operation enables Network Slice selection inboth the Serving PLMN and HPLMN. It also enables the NSSF to provide tothe AMF the Allowed NSSAI and the Configured NSSAI for the Serving PLMN.

It may be invoked during Registration procedure, during PDU SessionEstablishment procedure or during UE Configuration Update procedure.When invoked during Registration procedure it may possibly trigger AMFre-allocation. When invoked during PDU Session Establishment procedureit may be invoked in the VPLMN or in the HPLMN. When invoked during UEConfiguration Update procedure it may be invoked in the Serving PLMN.

The list of events, which trigger invoking of the Nnssf_NSSelection_Getservice operation, is not exhaustive.

Inputs, Required: None.

Inputs, Conditional Required:

If this service operation is invoked during Registration procedure nottriggered by mobililty from EPS to 5GS or UE Configuration Updateprocedure, then the following inputs are required: Requested NSSAI,Subscribed S-NSSAI(s) with the indication if marked as default S-NSSAI,PLMN ID of the SUPI, TAI, NF type of the NF service consumer, RequesterID.

If this service operation is invoked during Registration proceduretriggered by mobility from EPS to 5GS with N26 (as described in clause4.11.1.3.3), the following inputs are required: S-NSSAIs for the HPLMNassociated with established PDN connection, PLMN ID of the SUPI, NF typeof the NF service consumer, Requester ID.

If this service operation is invoked during PDN Connection Establishmentin the Serving PLMN in EPS by a PGW-C+SMF, the following inputs arerequired:

Subscribed S-NSSAIs for the UE, PLMN ID of the SUPI, NF type of the NFservice consumer, Requester ID.

Else, if this service operation is invoked during PDU SessionEstablishment procedure in the Serving PLMN then the following inputsare required: S-NSSAI, non-roaming/LBO roaming/HR roaming indication,PLMN ID of the SUPI, TAI, NF type of the NF service consumer, RequesterID.

Inputs, Optional:

If this service operation is invoked during Registration procedure nottriggered by mobililty from EPS to 5GS or UE Configuration Updateprocedure then the following inputs are optional (if available): MappingOf Requested NSSAI, Allowed NSSAI for current Access Type, Allowed NSSAIfor the other Access Type, and the corresponding Mapping Of AllowedNSSAIs.

If this service operation is invoked during PDU Session Establishmentprocedure then the following input is optional: HPLMN S-NSSAI that mapsto the S-NSSAI from the Allowed NSSAI of the Serving PLMN.

Outputs, Conditional Required:

If this service operation is invoked during Registration procedure nottriggered by mobility from EPS to 5GS or UE Configuration Updateprocedure, then one or more of the following outputs are required:Allowed NSSAI, Configured NSSAI; Target AMF Set or, based onconfiguration, the list of candidate AMF(s).

If this service operation is invoked during Registration proceduretriggered by mobility from EPS to 5GS with N26 (as described in clause4.11.1.3.3), the following output is required: S-NSSAIs for the HPLMNassociated with established PDN connection, Mapping of S-NSSAIsassociated with established PDN connection in the Serving PLMN.

If this service operation is invoked during PDN Connection Establishmentin the Serving PLMN in EPS by a PGW-C+SMF, the following outputs arerequired: Subscribed S-NSSAIs for the UE, Mapping of S-NSSAIs associatedwith the subscribed S-NSSAIs for the UE in the Serving PLMN.

Else, if this service operation is invoked during PDU SessionEstablishment procedure then the following outputs are required: The NRFto be used to select NFs/services within the selected Network Sliceinstance.

Outputs, Conditional Optional:

If this service operation is invoked during UE Registration procedure orUE Configuration Update procedure, then one or more of the followingoutputs are optional: Mapping Of Allowed NSSAI, Mapping Of ConfiguredNSSAI, NSI ID(s) associated with the Network Slice instances of theAllowed NSSAI, NRF(s) to be used to select NFs/services within theselected Network Slice instance(s) and NRF to be used to determine thelist of candidate AMF(s) from the AMF Set, rejected S-NSSAI with causeof rejection.

Else, if this service operation is invoked during PDU SessionEstablishment procedure, then the following output is optional: NSI IDassociated with the S-NSSAI provided in the input.

Appendix B from the Provisional Patent Application

The provisional patent application to which this application claimspriority included an Appendix B, which is reproduced in relevant partbelow:

Change Request

Reason For Change: For a UE being served by EPS and with established PDNConnections we have three different scenarios for a PDN Connection: (1)The UE is served in its home network; (2) The UE is served in a visitednetwork with home routed traffic; (3) The UE is served in a visitednetwork with LBO.

In all three cases, with surviving PDN connections when moving to 5GS,combined PGW-C+SMFs are used and during PDN Connection establishment theUE allocates respective PDU Session ID and sends it to the PGW-C+SMF viaPCO. An S-NSSAI associated with each PDN connection is determined basedon the operator policy by the PGW-C+SMF, e.g. based on a combination ofPGW-C+SMF address and APN, and sent to the UE in PCO together with aPLMN ID that the S-NSSAI relates to (refer to 23.501 clause 5.15.7.1).

When UE moves from EPS to 5GS, the UE includes the S-NSSAIs (with valuesfor the Serving PLMN of the target 5GS, if available) associated withthe established PDN connections in the Requested NSSAI in RRC ConnectionEstablishment and NAS. The UE also provides to the AMF in theRegistration Request message the mapping information as described inclause 5.15.6 (refer to 23.501 cl 5.15.7.2).

For case 1 and 2 the UE will get hS-NSSAI(s) (S-NSSAIs valid in the homenetwork) in the PCO from the combined PGW-C+SMFs.

For case 3 the UE will get vS-NSSAI(s) (S-NSSAIs valid in the visitednetwork) in the PCO from the combined PGW-C+SMFs.

Without checking that an allocated hS-NSSAI or vS-NSSAI (through itsmapped hS-NSSAI) is allowed, according to the UEs subscribed S-NSSAIs,there is a risk at mobility from EPS to 5GS that AMF needs to releasePDU Session(s) associated to S-NSSAI(s) not allowed according to the UEssubscribed S-NSSAIs. This is valid in case the PGW-C+SMF supports morethan one S-NSSAI and at least one of these are also allowed according tothe UEs subscribed S-NSSAIs

The question is then how such a combined PGW-C+SMF should ensure that anallocated hS-NSSAI or vSNSSAI is allowed according to the UEs subscribedS-NSSAIs?

For case 1 and 2 the combined PGW-C+SMF allocates an hS-NSSAI and wouldthen be required to check that the selected hS-NSSAI is among the UEssubscribed S-NSSAI. This could be achieved by letting the SMF use theNudm_SDM_Get (SUPI, Slice Selection Subscription data) service(currently only available to the AMF) to get the UEs subscribed S-NSSAIand only allocate hS-NSSAI among them. For case 1 and 2 the procedure inthe combined PGW-C+SMF should look like: (1) Fetch subscribed S-NSSAIs(hS-NSSAIs) from UDM; (2) Select a h-NSSAI from the hS-NSSAIs acquiredin step I and include it in the PCO to the UE at PDN connectionestablishment.

For case 3 the combined PGW-C+SMF allocates an vS-NSSAI and would thenbe required to check that the selected vS-NSSAI is mapped to an hS-NSSAIthat is among the UEs subscribed S-NSSAI. To get the subscribed S-NSSAIsthe same procedure as proposed for case 1 and 2 above can be used. Butto get the mapping between subscribed S-NSSAIs and correspondingvS-NSSAIs an adjustment of the Nnssf_NSSelection_Get service from theNSSF is needed. The service should be available from the PGW-C+SMF andas input/output it should be possible to provide subscribed S-NSSAI. Forcase 3 the procedure in the combined PGW-C+SMF should look like: (1)Fetch subscribed S-NSSAIs (hS-NSSAIs) from UDM; (2) Get correspondingvS-NSSAI for each subscribed S-NSSAI by querying the NSSF; and (3)Select a vS-NSSAI from the vS-NSSAIs acquired in step II and include itin the PCO to the UE at PDN connection establishment.

Summary Of Change: Let the PGW-C+SMF at PDN Connection establishmentonly allocate hS-NSSAI or vS-NSSAI (via mapped hS-NSSAI) that isallowed, according to the UEs subscribed S-NSSAIs.

Consequences if not approved: There is a risk at mobility from EPS to5GS that AMF needs to release PDU Session(s) associated to S-NSSAI(s)not allowed according to the UEs subscribed S-NSSAIs.

5.15.7 Network Slicing and Interworking with EPS

5.15.7.1 General

A 5GS supports Network Slicing and might need to interwork with the EPSin its PLMN or in other PLMNs as specified in clause 5.17.2. The EPC maysupport the Dedicated Core Networks (DCN). In some deployments, the MMEselection may be assisted by a DCN-ID provided by the UE to the RAN (seeTS 23.401 [26]).

Mobility between 5GC to EPC does not guarantee all active PDU Session(s)can be transferred to the EPC.

During PDN connection establishment in the EPC, the UE allocates the PDUSession ID and sends it to the PGW-C+SMF via PCO. An S-NSSAI associatedwith the PDN connection is determined based on the operator policy bythe PGW-C+SMF, e.g. based on a combination of PGW-C+SMF address and APN,and is sent to the UE in PCO together with a PLMN ID that the S-NSSAIrelates to. The PGW-C+SMF should only select an S-NSSAI that is mappedto an S-NSSAI among the subscribed S-NSSAIs of the UE. The UE storesthis S-NSSAI and the PLMN ID associated with the PDN connection. The UEderives Requested NSSAI by taking into account of the received PLMN ID.The Requested NSSAI is included in NAS Registration Request message andRRC carrying this Registration Request when the UE registers in 5GC ifthe UE is non-roaming or the UE has Configured NSSAI for the VPLMN inroaming case.

While various embodiments of the present disclosure are describedherein, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent disclosure should not be limited by any of the above-describedexemplary embodiments. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by thedisclosure unless otherwise indicated herein or otherwise clearlycontradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

1. A method performed by a User Equipment (UE) during establishment of apacket data connection, the method comprising: transmitting to a sessionmanagement node supporting interworking between a first system and asecond system a message requesting establishment of the packet dataconnection in the first system; and receiving from the sessionmanagement node a network slice identifier, wherein the network sliceidentifier is selected by the session management node from either i) asubscription set of network slice identifiers or ii) a second set ofnetwork slice identifiers corresponding to a mapped set of thesubscription set of network slice identifiers.
 2. The method of claim 1,wherein the message requesting establishment of the packet data sessionfurther comprises a session identifier identifying a connection betweenthe UE and a data network, and the selected network slice identifieridentifies a network slice that can support the connection between theUE and the data network when the UE is handed over from the first systemto the second system.
 3. The method of claim 1, wherein the sessionmanagement node is a combined Session Management Function (SMF) andPacket Data Network Gateway-Control (PGW-C).
 4. The method of claim 1,wherein the first system is an evolved packet system (EPS) and thesecond system is a 5th Generation System (5GS).
 5. A computer programproduct comprising a non-transitory computer readable medium storing acomputer program comprising instructions which when executed byprocessing circuitry of a User Equipment (UE) causes the UE to performthe method of claim
 1. 6. A User Equipment (UE), the UE comprising:processing circuitry; and a memory, the processing circuitry beingconfigured to access data stored in the memory, wherein the UE isconfigured to: transmit to a session management node supportinginterworking between a first system and a second system a messagerequesting establishment of a packet data connection in the firstsystem; and receive from the session management node a network sliceidentifier, wherein the network slice identifier is selected by thesession management node from either i) a subscription set of networkslice identifiers or ii) a second set of network slice identifierscorresponding to a mapped set of the subscription set of network sliceidentifiers.
 7. The UE of claim 6, wherein the message requestingestablishment of the packet data session further comprises a sessionidentifier identifying a connection between the UE and a data network,and the selected network slice identifier identifies a network slicethat can support the connection between the UE and the data network whenthe UE is handed over from the first system to the second system.
 8. TheUE of claim 6, wherein the session management node is a combined SessionManagement Function (SMF) and Packet Data Network Gateway-Control(PGW-C).
 9. The UE of claim 6, wherein the first system is an evolvedpacket system (EPS) and the second system is a 5th Generation System(5GS).
 10. A method comprising: a session management entity storing twoor more supported network slice identifiers, wherein the sessionmanagement entity is in a serving network and supports interworkingbetween a first system and a second system; the session managemententity retrieving, from a network node function, a set of first networkslice identifiers; the session management entity selecting a supportednetwork slice identifier from among the stored two or more supportednetwork slice identifiers based on the set of first network sliceidentifiers; and the session management entity transmitting, to the UE,information indicating the selected supported network slice identifier,wherein when the set of first network slice identifiers are a set ofsubscribed network slices, the network node function is a user datamanagement function and the serving network is a home network of the UE,and when the set of first network slice identifiers are a set of mappedsubscribed network slices to network slices supported by the servingnetwork, the network node function is a network slice selectionfunction, and the serving network is a visited network by the UE. 11.The method of claim 10, wherein the method further comprises the step ofreceiving, from the UE, a session identifier identifying a connectionbetween the UE and a data network, the information transmitted to the UEindicates that the selected network slice identifier is associated withthe connection between the UE and the data network established over thefirst system, and the selected network slice identifier identifies anetwork slice that can support the connection between the UE and thedata network when the UE is handed over from the first system to thesecond system.
 12. The method of claim 10, wherein the sessionmanagement entity is a combined Session Management Function (SMF) andPacket Data Network Gateway-Control (PGW-C).
 13. The method of claim 10,wherein the first system is an evolved packet system (EPS) and thesecond system is a 5th Generation System (5GS).
 14. A computer programproduct comprising a non-transitory computer readable medium storing acomputer program comprising instructions which when executed byprocessing circuitry of a session management entity causes the sessionmanagement entity to perform the method of claim
 10. 15. A sessionmanagement entity in a serving network supporting interworking between afirst system and a second system, the session management entitycomprising: processing circuitry; and a memory, the processing circuitrybeing configured to access data stored in the memory; wherein thesession management entity is configured to: store two or more supportednetwork slice identifiers; retrieve from a network node function, a setof first network slice identifiers; select a supported network sliceidentifier from among the stored two or more supported network sliceidentifiers based on the set of first network slice identifiers; andtransmit, to the UE, information indicating the selected supportednetwork slice identifier, wherein when the set of first network sliceidentifiers are a set of subscribed network slices, the network nodefunction is a user data management function and the serving network is ahome network of the UE, and when the set of first network sliceidentifiers are a set of mapped subscribed network slices to networkslices supported by the serving network, the network node function is anetwork slice selection function, and the serving network is a visitednetwork by the UE.
 16. The session management entity of claim 15,wherein the session management entity is further configured to receive,from the UE, a session identifier identifying a connection between theUE and a data network, the information transmitted to the UE indicatesthat the selected network slice identifier is associated with theconnection between the UE and the data network established over thefirst system, and the selected network slice identifier identifies anetwork slice that can support the connection between the UE and thedata network when the UE is handed over from the first system to thesecond system.
 17. The session management entity of claim 15, whereinthe session management entity is a combined Session Management Function(SMF) and Packet Data Network Gateway-Control (PGW-C).
 18. The sessionmanagement entity of claim 15, wherein the first system is an evolvedpacket system (EPS) and the second system is a 5th Generation System(5GS).